Precipitation behavior during hot deformation of powder metallurgy Ti-Nb-Ta-Zr-Al high entropy alloys

Refractory high entropy alloys with compositions of TiNbTa0.5Zr and TiNbTa0.5ZrAl0.2 were prepared by powder metallurgy. The alloys were hot deformed at 800 °C with a strain rate of 0.001s−1. The microstructural evolution, precipitation behavior and flow behavior at different compressive strain were investigated. Results show that the alloys are single BCC phase. The hot deformation induces precipitation both in grain boundaries and inside grains. The critical compressive strain for intragranular precipitation of TiNbTa0.5Zr and TiNbTa0.5ZrAl0.2 alloys is 20% and 10%, respectively. The precipitates are BCC phase and enriched with Nb and Ta, while the deformed matrix is enriched with Zr. A bi-modal grain size microstructure with micro-scaled intergranular precipitates and nano-scaled intragranular precipitates is achieved after being deformed to 50%. The precipitation leads to a significant flow softening during deformation. And after hot deformation, the TiNbTa0.5ZrAl0.2 alloy has a compressive yield strength of 1500 MPa with a high compressive strain of 18% at room temperature, mainly due to the bi-modal grain size microstructure.